OCEANOGRAPHY IN THE UNITED STATES 29 



The next slide shows the locations of our wave gage stations. "We 

 have had about 30 over the last 10 years and we have about 7 in 

 operation now. Some of our larger inland lakes have them and some 

 of our inland reservoirs. 



The next slide. On the subject of wave action before it begins to 

 move the bottom materials, we have published these technical memo- 

 randums. Here is a sample, an analysis of wave generation by 

 moving storms such as hurricanes or northeasters; change of wave 

 height by bottom friction; wave variability and wave spectra; model 

 study of laws of wave refraction. 



The next slide, I think, will show some of the results that we have 

 gotten from these studies. 



This shows briefly the variation in the type of wave spectra witli the 

 type of generating storm. We found tliat if the storm was moving 

 rapidly we got one kind of spectrum. If it was stationary we got 

 another type. 



This set of curves enables the forecaster to predict the type of 

 spectrum he is going to get out of a particular wave generating area. 

 Next slide. Tliis looks like a liurricane wind pattern. Actually it 

 is a hurricane pattern but it is a pattern of waves generated by the 

 hurricane instead of the wind pattern. You notice the similarity 

 in the contours, you might say. These are contours of wave height 

 instead of wind pressure or wind velocity. 



The next slide. This shows the study we made to find out how 

 much energy is taken out of the wave as it moves into shallow water 

 due to percolation of the water into the bottom. We had some theory 

 wliich showed tluit this would be the condition on the particular test. 



We found, however, that the theory indicated about twice as 

 much loss as actually was the case so that we have now adjusted the 

 constants in the theoretical formula to give us a more accurate answer 

 to tliis particular action. 



The next slide. As the waves moves on into the shore it begins to 

 move the sand around and it is tlie movement of this sand on the 

 shore that constitutes the basis of most of our shore erosion problems. 



A few of our technical memorandums are as follows: 



"Sand Movement Near Anaheim Bay, Calif.", was a field study. 



"Mechanics of Bottom Sediment Movement." This is the fun- 

 damental mechanics made in a tank at MIT. 



"Sand Movement Around Southern California Promontories." 

 In California it was thought that the rock promontories actually 

 blocked the movement of sand along the shore. We found that wave 

 action was able to transport the sand in 20 or 30 feet of water, and 

 move it around these promontories. 



"Ripples in Nearshore Sands." These have some effect. 



The next slide will show you some of the actual results. 



This was a study to find out the conditions that caused the offshore 

 bars to form. We found that the more regular the waves, that is, if 

 we had waves of a definite period and only definite waves, we got the 

 bars formed rapidly. If we put in a varying set of waves we ironed 

 out these various offshore bars. 



Next slide. Tliis was a particularly interesting study to try to 

 correlate the wave energy reaching the shore and the rate of sand that 

 was pushed along the shore face. 



We had quite a number of observations in our small tanks but with 

 soine considerable difficulty we finally got four points at Palm Beach, 



